Pneumotachs, or pneumotachographs, as they are sometimes called, have long been known in the art. They are primarily flow-sensing devices, whose output is in the form of a pressure signal proportional to the rate of air flow. Prior art devices have generally involved keeping pressure taps of air flow at different locations along a tube, with the pressure differential between the taps used as an indication of flow measurement. However, in such prior art devices, the change in pressure is a function of the square of the velocity of flow. When the device is used to measure breathing, especially in the instances where pulmonary problems are present, the flows can vary from very low flow rates to very high flow rates, and especially covering ranges of, for example 250 to 1. Once these flow velocities are squared, the ratio becomes 62,500 to 1, thereby introducing inaccuracies.
It is also known that it is desirable to measure laminar flow, as distinguished from turbulent flow, because the pressure measurement becomes a linear, not a second-degree function. However in many devices seeking to measure laminar flow, tubes or the like are inserted into the flow tube, leading to additional inaccuracies caused by moisture, phlegm from coughing, or similar sources, which causes condensation and blockage, and in any event produces erratic measurements.
Additionally, while both visually-read spirometric measurements and visually-read pneumotach measurements have been known, it is not believed that these measurements have heretofore been combined in a readily accessible kit, in accordance with the present invention.